In general, a data recording and reproduction apparatus using a hologram records and reproduces information in a recording medium using a diffraction of light and interference effects of light, and generally uses an interference pattern generated due to an interference between signal light and reference light. The interference pattern (that is, holographic data) formed in this manner is recorded in the recording medium When the recording medium in which the interference pattern has been stored is irradiated with the reference light, the interference pattern stored in the recording medium is reproduced, and recorded data is reproduced.
In this case, the holographic data recorded in the recording medium can be read using only the reference light used in a recording process. The holographic data is not read using reference light having a different wavelength or phase from the reference light used at the time of recording, and such reference light passes through the holographic data recorded in the recording medium. By recording and multiplexing a large amount of holographic data at the same place of the recording medium with different reference light using such properties of the hologram, a large amount of data can be stored in a small recording medium. Here, the data is processed in units of predetermined pages. Data in page units is called a data page, and the data page includes a plurality of pixels represented by data bits.
In particular, in the case of a holographic recording medium, two-dimensional inter symbol interference ((2D-ISI) due to a diffraction effect caused by recording light source interference) mainly degrades storage quality according to characteristics that data is processed in units of pages.
Meanwhile, when data recorded on the recording medium is reproduced, a bit error rate (BER; a failure rate of restoration to original data) should be reduced such that the data can be reproduced without being lost. However, when multiplexed holographic data is reproduced, a probability of erroneous bit detection increases due to the two-dimensional inter symbol interference described above and a narrow data page detection area.
Conventionally, for accurate data reproduction, a preset threshold value is applied en bloc so as to determine an output value of each pixel. Accordingly, there is a problem in which accuracy is degraded in data reproduction.